1. Field of invention
This invention relates to automated blood or liquid analysis systems and, more particularly, to an apparatus and method for automatically withdrawing and testing blood or other liquids.
2. Prior Art
As known for years, the treatment of patients who are critically ill with respiratory or cardiovascular disorders require frequent measurement of various blood parameters such as pH, pO.sub.2, pCO.sub.2, HB, HCO.sub.3, TCO.sub.2, BE, SBE, SatO.sub.2, and SBC. While oxygenation is necessary for the maintenance of life, it is also important to reduce the duration of high oxygen concentration to a minimum in order to prevent possible toxic effects in the lungs. There are numerous other situations, such as in diagnosis of critical illness, patient monitoring during certain corrective procedures and intensive care programs wherein blood parameters must be frequently measured, analysed and controlled.
However, frequent manual withdrawal of blood is undesirable due to the increased opportunity for the entrance of air emboli in the blood stream. Similarly, multiple usage of an indwelling catheter requires re-arrangement of external tubing to adjust between blood withdrawal and irrigation configurations, which is subject to human error and which also presents increased incidence of air emboli infusion. Some systems known to the art return the analyzed blood to the patient after the measuring cycle, which procedure can create some possibility of patient contamination. On the other hand, systems known to the art which discharge withdrawn blood to waste after analysis thereof have utilized blood samples of an excessive volume. Other systems subject the patient to a risk of electric shock due to a continuous contact existing between the patient and electric potentials within the blood testing equipment or sensors. Also, systems which return blood to the patient cannot be used for destructive tests, such as glucose analyses, flame photometry etc...
Saline solution is commonly used as a compatible vehicle for use in blood pumps and tubing systems of blood test units, since some of its chemical properties approach that of blood. However, some blood parameters differ markedly from saline solution and pure water, which are used for cleaning a blood analysis system, and this may require a test principle which includes a slow process, such as diffusion across a membrane. Also, any repetitive usage of an accurate blood analysis system requires washout between samples. An efficient usage of such a system requires a rather rapid analysis cycle. Most blood analysis units known to the art require manual cleaning and/or manual calibrations between samples.